The dangers and costs involved by the presence of a very large number of birds, particularly domestic pigeons, in large centers of population, are known. Besides diseases, particular viral diseases, transmitted to man by air, domestic pigeons and starlings cause serious defacement of buildings, vehicles, roads, etc. by their droppings. Further, the cries and clucking of these birds considerably disturb the tranquillity of the citizens.
To mitigate these drawbacks, various types of processes or systems have been marketed or designed.
According to a first group of techniques, an effort is made to drive off the pigeons by placing a repulsive product, of the bird lime type, on all projections frequented by the birds. This process has numerous drawbacks inherent both in the product used (melting and running in hot weather, freezing in cold weather, attraction of dust and pollutants, short life) and in the difficulties and danger for workers and service personnel in applying it.
According to another group of systems, it has been proposed to place, on all the elements usually frequented by the birds, various devices intended to prevent them from alighting on the latter, such as, for example: inclined planes or strips of triangular shape with the point upward, folded like an accordion; triangular vertical plates brought close together, with sharp points, in the same plane or divergent; supports provided with pointed plastic teeth; sharp wires; etc. While such systems may be effective, at least in some cases, in causing the birds to lose their balance, they are not a panacea; actually, experience shows that birds apparently are not frightened by such devices with sharp points and avoid the difficulty by alighting in the immediate vicinity.